Add hero/banner-overlay CSS variables and wire template.css

- Add HERO / BANNER OVERLAY section to light.standard.css and dark.standard.css:
  --hero-height, --hero-color, --hero-bg-repeat, --hero-bg-attachment,
  --hero-bg-position, --hero-bg-size, --hero-border-bottom,
  --hero-overlay-bg (light: 0.1 alpha / dark: 0.3 alpha),
  --hero-overlay-padding, --hero-overlay-text-align, --hero-overlay-text-color
- Replace all hardcoded values in .container-banner .banner-overlay and
  .overlay with var() references (with fallbacks)
- Fix background-position: comma syntax → correct space-separated single-bg value
- Add css_vars_hero note field to CSS Variables tab in templateDetails.xml
- Add TPL_MOKOCASSIOPEIA_CSS_VARS_HERO_LABEL/DESC to en-US and en-GB
- Regenerate .min files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/media/css/theme/dark.standard.css

@@ -520,6 +520,19 @@ color-scheme: dark;
 --gab-gray1: #868e96;
 --gab-gray2: #adb5bd;
 --gab-gray3: #ced4da;
+
+/* ===== HERO / BANNER OVERLAY ===== */
+--hero-height: 70vh;
+--hero-color: var(--body-color);
+--hero-bg-repeat: no-repeat;
+--hero-bg-attachment: fixed;
+--hero-bg-position: top center;
+--hero-bg-size: cover;
+--hero-border-bottom: solid var(--accent-color-secondary);
+--hero-overlay-bg: hsla(0, 0%, 0%, 0.3);
+--hero-overlay-padding: 1em;
+--hero-overlay-text-align: center;
+--hero-overlay-text-color: var(--body-color);
 }
 
 .btn {